Proteolysis of the ABri and ADan peptides by insulin degrading enzyme.

MORELLI,L.; LOVERA, RE.; FRANGIONE, B.; GHISO, J.; CASTAÑO, EM

San Diego

Congreso; Annual Meeting Society for Neuroscience; 2004

Familial British dementia (FBD) and Familial Danish dementia (FDD) are autosomal dominant disorders characterized by cerebrovascular and parenchymal amyloid deposition and neurofibrillarydegeneration. In both disorders, genetic defects result in the loss of the normal stop codon in the precursor BRI, generating novel peptides of 34 residues named ABri and ADan in FBD and FDD, respectively. ABri and ADan show a strong tendency to aggregate into non-fibrillar and fibrillar structures at neutral pH and such property seems to be directly related to neurotoxicity. Here we report that a recombinant insulin degrading enzyme (rIDE) is capable of degrading ABri and ADan in vitro. In the case of ABri, the presence of an intra-molecular disulfide bond strongly influenced susceptibility to degradation, as assessedwith a ABri-4-vinyl pyridine derivative and ABri peptides with Ser substitutions at Cys5 and Cys22. In addition, the 11-residue C-terminal extensions in both peptides rendered them more resistant to proteolysis as compared to the BRI wild-type product of 23 amino acids. Peptides with random conformation were readily degraded as opposed to species with structure and SDS-stable oligomerization, that were largely resistant to proteolysis by rIDE. Common sites of cleavage in ABri and ADan were Cys5-Phe6, Lys14-Phe15 and Leu20-lleu21, consistent with the known preference of IDE for basic or hydrophobic residues at position P1´. In addition, specific sites in ABri (Lys27-Lys28) and ADan (Phe23-Asn24) located at the C-terminal pathogenic extensions raise the possibility that proteolysis by IDE of soluble precursors may delay ABri and ADan aggregation in vivo.